1. Field of the Invention
The present invention relates to an optical reproducing device for reproducing information by irradiating a converged light beam to a record medium and detecting light reflected from the record medium or light transmitted therethrough. The present invention also relates to an optical reproducing method using the device and an optical record medium used in the device.
2. Description of the Related Art
In recent years, optical record media dedicated for reproducing information have played an important role for storing voice information data, video information data, and various other information data, because of their large capacity. Under this circumstance, an optical record medium having a larger capacity end a smaller-sized optical reproducing device have been demanded. In order to satisfy these demands, the recording density of a record medium should be increased.
A conventional optical reproducing-only device is described, lot example, in U.S. Pat. No. 4,332,022. An optical record medium used in this device includes a resin substrate in a disk shape and a reflective film made of aluminum or the like. The resin substrate has information tracks on its surface (an information carrier), consisting of concave or convex pits formed in a spiral shape or a concentric shape, and the reflective film is formed over the information carrier on the substrate by sputtering and the like. The recording density of this type of record medium is determined by the pitch of the information tracks and recording density in each track direction, i.e., linear density of information. Thus, in order to increase the recording density of the record medium, it is required that the track pitch is made smaller and/or the linear density is increased.
However, in the conventional record medium, when the track pitch is decreased, crosstalk from adjacent tracks is increased; when the linear density is increased, the interference among pits is increased. In order to overcome these problems, the spot size of a light beam irradiated to the record medium needs to be regulated. On the other hand, the track pitch and linear density are determined by the spot size. Thus, the regulation of a recording density is restricted by the spot size of a light beam which is suitable for preventing the crosstalk from adjacent tracks and the interference among pits.